1. Field of the Invention
The present invention relates to a metal anode for electrochemical processes, particularly for electrolytic processes, consisting of a metal resistant to the electrolysis medium and an active cover layer applied thereon, said layer containing the substances facilitating the electrode process.
2. Prior Art
Technical anode materials have to meet a number of requirements. For reasons of durability, the anode material must be sufficiently corrosion-resistant, and it must also be possible to carry out the anode process at sufficiently high speed. In the case of coated electrodes, the electron conductivity of the anode core and the surface layer, due to energy reasons, must be high and the excess voltage of the anode process must be low. Possible corrosion products of the anode may not disturb the normal operating course of the electrolytic process. Furthermore, the anode material should of course be inexpensive.
German patent application No. 1,813,944, published for inspection, describes a metal anode having an active cover layer on the basis of non-daltonoid, metallic conductive compounds of the type Me(I).sub.approx. 0.5 Pt.sub.3 O.sub.4 with Me(I) representing monovalent metals, e.g. Li or Na. Besides these materials, the cover layer may still contain binders, stabilizers and materials improving conductivity, e.g. TiC and/or TiN. The base member (core) of the anodes in this case consists either of a passivatable metal, e.g. titanium, tantalum, etc., or of a metal from the platinum group, or of a plated metal, e.g. copper/titanium, copper/tantalum, copper/platinum metal, titanium/platinum metal, tantalum/platinum metal, etc.
In this case of the cubic crystallizing compounds of the type Me(I).sub.approx. 0.5 Pt.sub.3 O.sub.4, the platinum atoms are squared planar and are surrounded by four oxygen atoms, and the coordination squares are stacked above one another as in the column structure. A platinum-platinum-chains obtained in this way are oriented in all three spatial directions. The individual platinum-platinum-chains are bonded through common oxygen atoms. In the centers of the oxygen cubes existing by the connection remains space for one Me(I)-cation. This bonding principle already provides for very short metal-metal-spacings, so that for each individual case the influence of the metal-metal-bond can only be assessed with great difficulty. In the case of the alkali metal platinates, the reduction of the alkali content, which leads to an increase of the formal oxidation stage of the platinum, appears to increase the platinum-platinum-bond proportions.
However, it is a prerequisite that the radii of the monovalent ions are not too large for the free gate locations to be occupied in size of about 1.2 A. This value is within the range of the ion radii of potassim, silver(I) and thallium(I), whereas the ion radii of lithium and sodium are smaller.